Sioux Falls Water Is Very Hard — Here's What It Costs You Each Year

Why Is Sioux Falls Water So Hard?

Sioux Falls gets its water from the City of Sioux Falls Water Division’s Main System, which blends water from the Missouri River with local groundwater. That combination is the whole story behind your 14.6 GPG (250 ppm) reading. The Missouri River starts out as relatively soft surface water, but by the time it reaches eastern South Dakota it has traveled through and over a vast amount of limestone, dolomite, and other calcium-rich sedimentary rock. Rain and river water are naturally slightly acidic, and as that water flows over and through those carbonate rocks, it dissolves calcium and magnesium ions right out of the stone. That is the classic recipe for hardness, and it is not something the utility can just filter out cheaply.

The groundwater portion of the blend makes things worse. The aquifers beneath the Sioux Falls area sit in the same kind of carbonate geology, and groundwater has far more contact time with the rock than surface water does. Water that sits underground for years or decades has had ample opportunity to dissolve minerals, so those wells pull up water that is often significantly harder than the river water. When the utility blends the two sources to meet demand, you get a finished product that lands squarely in the “very hard” category at over 10.5 GPG. The USGS classifies anything above that threshold as very hard, and at 14.6 GPG you are roughly double the national average of about 7.3 GPG. You are not imagining it if your glasses spot and your showerheads clog faster than they did somewhere else you have lived.

It is worth understanding that hardness is not a health hazard. The EPA does not regulate it as such; it only falls under the Secondary Maximum Contaminant Level, which is purely aesthetic. That means the city is not required to remove it, and they do not. The minerals stay in the water all the way to your tap. What that means practically is scale. According to the DOE, just a quarter inch of scale buildup can cut water-heater efficiency by up to 40 percent, and the Battelle Memorial Institute and WQRF found that hard water costs roughly 4 percent in gas water-heater efficiency for every 5 GPG of hardness in a typical 50-gallon-per-day household. At 14.6 GPG, you are looking at scale forming faster and thicker than it would in most of the country, and that scale is what drives up energy bills and shortens the life of any appliance that heats water. The WQA estimates that hard water shortens water-heater service life by about 30 to 50 percent, and their industry estimate is that the total cost of hard water across energy, appliance wear, and extra cleaning products adds up to a real chunk of change each year. You can get a dollar figure tailored to Sioux Falls from the calculator on this page, but the short version is that the minerals in your water are actively working against your plumbing and your wallet.

How Sioux Falls Compares to Nearby Cities

Sioux Falls sits at 14.6 GPG, which puts it on the harder end of the spectrum for the region. Rapid City, to the west, draws its water from a completely different source, groundwater wells in the Madison and Minnelusa aquifers that run through the Black Hills. That water also picks up minerals from the surrounding limestone and sandstone, but the geology there is different enough that you cannot assume the numbers match Sioux Falls. Watertown, to the north, relies on groundwater from the Big Sioux aquifer, and that source is similarly mineral-rich, though again the exact hardness depends on which wells are active and how the water is treated.

Omaha and Minneapolis give you the most useful comparison because both are major Missouri River cities, but they are not identical to Sioux Falls. Omaha draws from the Missouri River as well, and it deals with the same fundamental issue of river water running through carbonate geology. Minneapolis, by contrast, pulls most of its water from the Mississippi River, which has a different watershed and different mineral content. The Mississippi in that stretch tends to produce softer water than the Missouri, which is part of why Minneapolis water is generally easier on plumbing than what you get in Sioux Falls. None of these cities are drawing from a single shared aquifer, so the honest comparison is that Sioux Falls is on the high side for the region, and the Missouri River influence plus the local groundwater blend is what pushes it there. If you have lived in Minneapolis and thought the water felt different, you were right. If you have lived in Omaha or Watertown and thought it felt similar, that makes sense too, because you were all drinking water that had been soaking in the same kind of mineral-rich rock.

How does Sioux Falls stack up against the rest of South Dakota? It's very hard at 14.6 GPG — Watertown sits nearby. See the full hardest-water ranking for context.

See where Sioux Falls sits on the South Dakota water hardness map →

Want the broader explainer on what hardness actually is and how it behaves? Read hard water vs. soft water, explained.